Significant developments in web rewinding have placed ever-increasing product output demands upon web rewinders. Conventional web rewinders are capable of winding a roll or “log” of material in seconds, with maximum winding speeds determined by the strength and other properties of the web and the core upon which the web is wound. Such rewinders are generally limited in their ability to control the position and movement of cores through the rewinder nip, and therefore have limited control over web separation (where cores or core insertion devices perform web separation) and web transfer to new cores. As used hereinafter and in the appended claims, the term “nip” refers to an area between two winding elements, such as between two winding rolls, a winding roll and conveyor belt, two facing conveyor belts, or other elements known to those skilled in the art used to rotate and wind a log therebetween.
The nip can include an area disposed from the narrowest point between two winding elements, such as when a three-roll winding cradle is employed. The term “web” as used herein and in the appended claims means any material (including without limitation paper, metal, plastic, rubber or synthetic material, fabric, and the like) which can be or is found in sheet form (including without limitation tissue, paper toweling, napkins, foils, wrapping paper, food wrap, woven and non-woven cloth or textiles, and the like). The term “web” does not indicate or imply any particular shape, size, length, width, or thickness of the material.
Although faster rewinding speeds are desired, a number of problems arise in conventional rewinders when their maximum speeds are approached, reached, and exceeded. Specifically, the position and orientation of cores entering the winding nip is important to proper web transfer and web separation, but is often variable especially at high rewinder speeds. In some rewinders, a rewinder element separates the web either by pinching the web (thereby creating sufficient web tension between the pinch point and the downstream winding roll to break the web) or by cutting the web. The position and orientation of the core in such rewinders is important to ensuring that the newly-separated web begins to wrap around the core without wrinkling or web damage.
In many conventional rewinders, the web is separated into a trailing edge and a leading edge by a web separating device once the rewound log reaches a predetermined size or sheet count. The trailing edge of the web is wound around the nearly completed log, while the leading edge of the web is wound around a new core that has been positioned near the winding nip. The types of web separating devices vary in form, shape, type of motion and location within the rewinder. In some rewinders, the web is separated by effectively slowing or stopping the motion of the advancing web with the web separating means, thereby causing the web to separate downstream of the web separating means and upstream of the nearly completed log. This type of separation causes the web upstream of the web separating means to develop slack, thus complicating winding of the leading edge of the separated web onto a new core. This type of separation, however, can still be useful depending on the distance between the nearly completed log and the web separating means. If this distance is large relative to the distance between perforations (if a perforated web is employed) reliability and accuracy of web separation can be compromised. In other types of rewinders, the web is separated by effectively speeding up the motion of the advancing web with the web separating means, thereby causing the web to separate upstream of the web separating means.
In light of the limitations of the prior art described above, a need exists for an apparatus and method for a web rewinder in which sufficient core control is maintained to accurately and consistently insert and guide cores toward a rewinder nip, webs can be wound at very high speeds without winding errors, web material can be properly transferred to a newly inserted core, and predictable and reliable web separation is enabled even though significantly different web materials and types are run in the rewinder. Each preferred embodiment of the present invention achieves one or more of these results.